Room: Stars at Night Ballroom 1
Purpose: To develop a quality assurance (QA) system and to test the accuracy of delivering a stereotactic radiosurgery (SRS) / stereotactic radiotherapy (SRT) plan on a Linac, with ExacTrac verification and Hexapod correction.
Methods: The SRS MapCHECKâ„¢ (Sun Nuclear) is a 2D diode array with 2.47mm detector spacing. It was designed to be inserted into the StereoPHANâ„¢ (Sun Nuclear). A Brainlab mask was made for the StereoPHAN, referred to henceforth as mask StereoPHAN system (MSS). The MSS was then secured onto the Brainlab cranial head attachment on the Linac couch. With this setup, the Brainlab frameless Radiosurgery Positioning Array was used to enable ExacTrac (Brainlab) and Hexapod (Elekta) infrared tracking at any couch angle. The MSS was scanned with CT and imported into Brainlab patient specific QA software. The patient plans were created and mapped onto MSS. The MSS system was initially setup with lasers, and then more precisely positioned using ExacTrac and Hexapod prior to data acquisition and after each couch kick. After the plan was delivered, Gamma pass rates were analyzed in SNC patient software. To evaluate MSS system center accuracy in 3D, the SRS MapCHECK was positioned both horizontally and vertically.
Results: Five patients specific QAs were performed in this study. Gamma passing rates@3%/1mm criteria were: 99.8%, 95.9%, 93.2%, 96.8%, and 92.3%, respectively. The shifts calculated by SRS MapCHECK reflected the positioning accuracy using ExacTrac monitoring and Hexapod correction, which was 0.57Â±0.26mm in one direction, within the acceptable limit of 1mm. The QA results with the SRS MapCHECK in the horizontal and vertical positions were almost identical, which confirmed MSS center accuracy in all three dimensions.
Conclusion: The MSS system allowed us to not only test the dosimetry accuracy of the plan, but to also test ExacTrac verification and Hexapod correction.